1. Field of the Invention
The present invention generally relates to the forming of bump and lead circuits of the type which may be arranged on flexible tape and, more particularly, to mandrels used in producing such circuits and to the methods of fabrication thereof.
2. Description of the Prior Art
Carriers providing a bump circuit on one surface and a lead circuit on the other are well known in the art. They are used for making electrical contact with the terminals of semiconductor devices such, for example, as integrated circuit chips. The leads provide connections from the semiconductor terminals to other elements. The bumps or pads disposed on the surface opposite the lead circuit serve the purpose of facilitating contact with the semiconductor terminals. This is usually effected by a heat ram for thermally bonding the bumps to the terminals.
It is conventional practice to generate the lead and bump circuits by chemical etching. In other words, a plate of a suitable metal such as copper, for example, is subjected to chemical etching through a photoresist which has been illuminated through a mask and developed to expose the metal at places adjacent the bumps to be provided. As is disclosed in my prior U.S. Pat. No. 4,125,441, assigned to the assignee of the present application, a mandrel is formed which serves to act as a circuit former by providing cavities in which the etch resistant conductive material of the circuit is plated. To complete the fabrication process, the mandrel is finally etched away, leaving the bump circuit tape. Thus, in that process a new mandrel must be prepared for each new bump circuit which is produced.
Reference is made to a patent to Sanz et al, U.S. Pat. No. 3,350,250. This patent relates to a method of making printed wiring circuitry. Specifically, FIGS. 14-18 of the patent disclose a particular fabricating technique for a printed wire circuit. Here a temporary base member is drilled to provide a recess or indentation. This in turn is covered with a layer of conductive material to coat the recess. The conductive material forms a funnel-shaped protrusion which may be inter-nested with others to form electrically conductive interconnections. However, these protrusions are hollow.
Reference is also made to a patent to Pritikin, U.S. Pat. No. 2,692,190. It discloses various fabricating steps, again for making inlaid circuits. It should be noted that these inlaid or printed circuits are not provided with bumps.
The patent to Gigoux, U.S. Pat. No. 3,913,223, discloses a method of manufacturing a double-sided circuit, such as a printed circuit having raised through-hole eyelets shown particularly in FIGS. 3-5, 10 and 11. Basically an aperture is made in a laminated sheet which is then covered with metal to provide a through-hole eyelet. It should be noted that none of these patents relate to the type of bump and lead circuits on a tape to which the present invention is directed.
Other patents relate generally to various circuit fabrication techniques. Thus, the patent to Jackson, Jr., et al, U.S. Pat. No. 3,508,980, relates to an integrated circuit structure. It is made with dielectric isolation. Among others it discloses a chromium layer formed, for example, by vacuum evaporation deposition, which serves as a highly conductive region. This in turn will provide an ohmic contact to transistors.
The two patents to Carbonel, U.S. Pat. Nos. 3,583,066 and 3,566,461, both relate to a method of making a magnetic circuit element.
Finally, reference is made to a patent to Norton, U.S. Pat. No. 3,424,658, which also relates to a process of providing a printed circuit board on a metallic substrate. However, the circuit is not provided with any bumps which are essential to the circuitry provided by mandrels of the present invention.